Olivella pusilla (Marrat, 1871), Variations from Cape Romano, FL.

The following images are all of Olivella pusilla (Marrat, 1871) found at Pompano Hump, Cape Romano, Collier County, FL on 6/13/06. Since some of those examining this material believed some of these forms might be Olivella mutica, samples of all variations were provide to Dr. Harry Lee of Jacksonville for opinion. Dr. Lee confirmed all as Olivella pusilla, including the unusual banded color form.



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Wow, absolutely incredible images.

I stand corrected on my Pompano ID list.

Ok, so what are the key differences between pusilla and mutica?

Olivella mutica (Say, 1822)

I don't know why, but O. mutica is poorly treated. Apparently, Redfern did not find it in the Bahamas. DeJong and Coomans did not report it from Curacao, Aruba and Bonaire. Gunther Sterba does not even mention it in his Olividae A Collectors Guide. Abbott does treat it. Harry Lee has also provide some observations. So, let's see what they reported and compare it with O. pusilla. Here's a group image, a direct comparison with similarly colored O. pusilla, and a close up of the spire.

Group image of 7 O. mutica mmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmm Protoconch of O. mutica


O. mutica on each side; O. pusilla in middle.


Size: Per Abbott, O. pusilla goes as large as 9mm; O. mutica to 12mm. The mature speciments in the above image reflects that this is a significant difference. Harry indicates that O. pusilla is more slender and is less callused at the shoulder. This doesn't help with many of the immature specimens in the Cape Romano material.

Columella: Abbott reports that O. mutica has a strong, glossy callus on the parietal wall at the upper end. Both have such calluses, but the callus of O. mutica is obviously larger and extends farther posteriorly. Harry indicates O. pusilla usually has a darker brown tint to the columella and inner aperture and O. mutica has a less denticulate posterior columella.

Apex: Abbott describes the apex of O. mutica as "sharp." The protoconch of O. mutica clearly is more pronounced and extends upward as opposed to the small "bump" protrusion of the protoconch of O. pusilla that appears sunken in the first teleoconch whorl. This appears to me to be a key distinguishing character.

Sutures: Abbot does not mention the sutures of O. mutica, but indicates that the sutures of O. pusilla are narrowly channeled. To me, both appear to have deep, open, well defined sutures. However, the sutures of O. pusilla are very often partially hidden by an elevated, translucent ridge that runs around the top of each whorl.

Here's what I see:

Patterning: The color patterning of O. mutica is very characteristic in most specimens. On the body whorl there is a color band just below the suture with a jagged lower edge. Then, there is a narrow, white or lighter colored band (sometimes with pattering). Then comes a wide band of color that extends down to the top of the fasciole where there is another narrow, white or lighter colored band.

Overall shape: I'd describe O. mutica is more globose than Abbott's description of O. pusilla as "subelliptical to bullet-shaped." Another pronounced difference when observing the shells' teleoconch profile edge is that in O. pusilla each whorl above the body whorl is slightly inset so they appear to be "telescoping" one from the other; but the profile of the teleoconch of O. mutica is a smoothly curved line with breaks at the sutures.

Columella: The columella of O. mutica looks to me as distinctly concave versus the almost straight columella of O. pusilla.

Click here for more direct comparisons of O. mutica and O. pusilla.

Here's a little more, Marlo:

Olivella mutica (Say, 1822), the Variable Dwarf Olive, is a species which is well-named in the vernacular. Color forms range from solid chestnut to pure white, banding may be solid or netted (form fimbriata Reeve, 1850). Height of spire likewise quite variable. While this species and O. pusilla are often collected together, and range through most of FL to at least Bay Co., I know of no records for O. pusilla N. of St. Augustine. O. mutica is abundant N. to Cape Hatteras (HL; Porter and Houser, 1997; p. 89) and even reaches NJ (Merrill, Bullock, and Franz, 1978). Bahamas record (Abbott, 1974) needs confirmation. Egg capsules described by Payne (1962); newborns crawl away. A sinistral Pliocene specimen was reported by Campbell and Campbell (1976). This species swims using ample winglike extensions of its foot called metapodia (Bill Frank, pers. obs., 5/12/01). O. mutica and O. pusilla (Marrat, 1871), the Tiny Dwarf Olive, are closely related and variable species. Certain color forms create an uncanny interspecific resemblance, but O. pusilla usually has a darker brown tint to the columella and inner aperture. Furthermore, it is smaller, more slender, less callused at the shoulder, has a less denticulate posterior columella, smaller protoconch, and different egg capsule morphology (Perry and Schwengel, 1955; Payne, 1962). Rather scarce in E. FL, [St. Lucie and Palm Beach Cos. (HL)], but abundant and widespread the state’s Gulf coast. Sinistral specimen from Port St. Joe, FL. (HL).

Campbell, L. D. and S. C. Campbell, 1976. Sinistral specimens of Olivella, Prunum, and Granulina from the Pliocene of Virginia and North Carolina. The Nautilus 90(4): 151-152. Oct. 29.

Merrill, A. S., R. C. Bullock, and D. R. Franz, 1978. Range extension of mollusks from the Middle Atlantic Bight. The Nautilus
92(1): 34-40. Jan. 31.

Payne, R. T., 1962. Reproduction of Olivella mutica. The Nautilus 75(4): 139-141, April.

Perry, L. and J. S. Schwengel, 1955. Marine shells of the western coast of Florida. Revised edition. Paleontological Research
Institution, Ithaca, pp. 1-318 incl. 55 pls.

Porter, H. J. and L. Houser, [1997]. Seashells of North Carolina. North Carolina Sea Grant College Program, Raleigh, iv + pp. 1-
[133], numerous text figs. + 6 colored pls.

Harry G. Lee